Implement default values for storages

[Serchinastico]

We have been tracking a crash happening in the database (see #172 and its PR #175).

In order to solve it we are now capturing the exception and calling an optional ErrorListener the caller provides. Given we can't really do nothing about the issue, we are using that listener to return a default value in the case of the config, null otherwise.

We should try to pass a default value in case something happens instead so that it's easier to call.